3.5. Effect of tannic acid and EKWE on microstructure of fish emulsion sausages
Microstructures of the emulsion sausage samples added without and with tannic acid (0.02% and 0.04%) or EKWE (0.04% and0.08%) at day 20 of refrigerated storage are illustrated in Fig. 3.Emulsion sausages containing tannic acid or EKWE had the slightly compact structure with less voids. The control and EKWE added samples had the loosened structure with larger voids than the tannic acid added samples. After 20 days of storage, TA-0.04 sample had the highest hardness, gumminess and chewiness. This was reflected by more compact structure of the sample. Tannic acid at higher level might be involved in decreasing the growth of microorganisms, which more likely degraded the protein matrix. Also, tannic acid played a role as antioxidants, in which radicals or oxidation products, capable of destruction of matrix previously formed, could be lowered. For the distribution of oil droplets and formation of emulsion in the sausages, it was noticed that TA-0.04 sample contained continuously and homogenously dispersed oil droplets, which were smaller in size, compared to others (Fig. 3c). The compact matrix generally confers a greater consistency to the product and promotes hardness of the product .Tannic acid at a level of 0.04% might prevent the coalescence of emulsion through its protective role in retardation of the oxidative damage to the protein, which act as an emulsifier. Proteins have emulsifying properties, yielding the stable meat emulsion. The oxidative damage of proteins has an impact on protein solubility, leading to aggregation and complex formation due to cross links, thus impairing their emulsifying property .Phytochemicals such as lutein, ellagic acid and olive leaf extract might have increased the emulsion stability in the cooked pork sausage through their protective role on proteins against oxidation.Thus, tannic acid at level of 0.04% was effective in maintaining the textural properties of the fish emulsion sausages stored at refrigerated temperature for 20 days.
Acknowledgement
The authors would like to express their sincere thanks to the Graduate School of Prince of Songkla University and the National Research University project of Thailand’s Office of the Higher Education
Commission for financial support.